Studio Wildcard’s dinosaur game Ark: Survival Evolved is one of gaming’s biggest success stories in recent years. By the developer’s latest count, it’s sold 16 million copies across PC, Xbox One, and PlayStation 4, with ten million more installs on mobile where it’s free.

Part of what makes the game’s ongoing success so noteworthy is that the title does not offer loot boxes or skins, instead opting to sell big, premium expansions that help the game enjoy sustained revenue that funds future development.

Studio Wildcard co-founder Jesse Rapczak told GI.biz that Ark enjoys a “sustainable revenue model” by way of launching one or two major “premium updates” each year.

“We don’t sell skins, we don’t sell upgrade packs,” he said. “But Ark is an online game with official servers and a lot of costs to keep the game running. It’s important to us to always be bringing in new players, and part of that is creating new content for the existing ones so they bring in their friends.”

Ark has welcomed three expansions to date: Scorched Earth, Aberration, and Extinction. The next big one is called Genesis, and it will be released in two parts starting in Fall 2020.

Rapczak said he feels “a little bit justified” about the decision to release premium expansions instead of chasing microtransactions like many other big games do. “It feels good when people want to pay for what you’re creating, rather than them feeling like they’re getting nickeled, dimed and swindled a little, which is I think what happens when you have loot boxes and tack on those mechanics to something they’ve already paid for,” he said.

Free-to-play mechanics in full-price games can be problematic and challenging–for players and the developer alike, Rapczak said.

“If players have already paid for the game and you’re adding on these sorts of free-to-play mechanics, it’s kind of annoying,” he said. “And you’re also doubling your work, because you have to make sure the base game is great enough that people want to spend money on it, and then you also have to figure out how to entice them to spend further money on the game. I guess that’s why the big companies like EA, Ubisoft and whoever are willing to tackle that, but there’s been a lot of issues with that. For indies and medium-sized companies, it’s not the thing to try and pursue.”